From a standpoint of static electricity it is generally considered that the earth is electrically positive. Small particles generally, such as dust, smoke, organisms in the rooms of buildings, etc., tend to be positive. Such small particles tend to be repelled by the statically positive building structures and that earth and therefore to remain in suspension in the air. Breathing of such particles is undesirable.
It previously has been recognized that generation of negative ions will cause such positive particles of dust, smoke, etc., to be attracted to the ions, and to form sufficiently large particles physically that they will drop gravitationally to the earth or floor, as well as to be negatively charged for attraction to the earth, floor or walls. Negative ions also dispel static electricity which is often troublesome.
The foregoing has been recognized in the patent art, see for example U.S. Pat. Nos. 4,037,268 and 4,109,290, and the art of record therein.
There has also been a rather significant quantity of literature generated arguing as to the beneficial physiological effects of breathing negative ions in the air. Although the physiological effects are not universally accepted they may be considered as a possible bonus to the accepted physical effects of removing particulate material from the air.